Fix pane watcher audit regressions

[brickfrog]

Fixes Sarcasmotron audit receipt f2358fc8 for feature/pane-watcher-revival.

Closes audit finding 1 from receipt f2358fc8: apply_recovered_agent registered recovered agents but never reattached pane watching. Alive recovered agents with terminal targets now call watch_pane and the regression asserts watched_agents plus resolved pane id after recovery.

Closes audit findings 2 and 3 from receipt f2358fc8: pre-TDD leaf no-handoff still sent a LocalTerminalInput prod and the Prod/prodded_at machinery survived. The decision enum is now binary, pre-TDD escalates directly to the parent at the idle threshold, worker_no_handoff_prodded_at and reload serialization are deleted, and targeted tests assert nothing is sent to the leaf pane.

Closes audit finding 4 from receipt f2358fc8: src/runtime pane watcher used @exec through a native default. PaneWatcher::new is now hermetic with an empty host; the serve path continues injecting the native dump-screen adapter at the bin/server boundary, and src/runtime no longer imports choir/src/exec.

Closes audit finding 5 from receipt f2358fc8: missing host-observable live zellij dump-screen check. Added a self-skipping real exec integration test that creates a scratch tab only when ZELLIJ_SESSION_NAME points at a live session, resolves pane/tab ids, asserts dump-screen --pane-id returns text without changing query-tab-names output, and closes by tab id.

Also removes stale stop_subscribe naming in the pane-watch drop path.

Verified:

• moon test --target native
• moon build src/bin/choir_lint --target native && _build/native/debug/build/src/bin/choir_lint/choir_lint.exe
• moon info --target native
• ! grep -rEn "WorkerNoHandoffDecision::Prod|worker_no_handoff_prodded_at|leaf_pre_tdd_stall_prod_text|_prod_text" src/
• ! grep -rEn "@exec.|choir/src/exec" src/runtime/
• moon fmt

Verification

Generated by Choir from commands executed in the leaf workspace.

• moon test --target native
  • exit: 0
  • head: 55590e4
  • output tail:

Warning: Main package `choir/src/bin/choir` uses blackbox-only test inputs (`_test.mbt` files) in package directory "/mnt/data/Code/choir/.choir/worktrees/pane-audit-fix-1781353854343-11308-0/src/bin/choir". Main packages will stop generating blackbox tests in a future release. Move public behavior into a non-main package and keep the main package as an entrypoint.
4
Total tests: 2009, passed: 2009, failed: 0.

• moon build src/bin/choir_lint --target native && _build/native/debug/build/src/bin/choir_lint/choir_lint.exe
  • exit: 0
  • head: 55590e4
  • output tail:

Finished. moon: no work to do

• ! grep -rEn "WorkerNoHandoffDecision::Prod|worker_no_handoff_prodded_at|_prod_text" src/

  • exit: 0
  • head: 55590e4

• ! grep -rEn "@exec\.|choir/src/exec" src/runtime/

  • exit: 0
  • head: 55590e4

[brickfrog]

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